Arena Pharmaceuticals Inc. (ARNA) and Eisai Co. (ESALY, 4523.TO) said that a study of the diet pill lorcaserin showed that the drug seems to concentrate in the human brain less than it does in rats.
The data is part of the companies' work to respond to Food and Drug Administration concerns that led to the pill being rejected for approval last year. The agency requested multiple sets of new data including studies related to breast cancer and brain cancer occurring in rats, and more information on heart-related risk.
Shares of Arena recently traded up 4.4% to $1.66 amid a broader market sell-off. Several analysts said the data appeared to be positive, but that the focus for investors is the FDA's concerns about breast cancer in rats and whether its can convince regulators to allow the drug on the market.
"We continue to be concerned about the high level of residual regulatory risk with lorcaserin," Jefferies analyst Thomas Wei said in a note to clients. An Arena spokesman said that its "development plan and timeline remain on track" and the company plans to submit a response to the FDA by year-end. A three-month study to address the breast cancer issue is ongoing, he said.
Arena conducted the study by measuring lorcaserin concentrations in human cerebrospinal fluid and then seeing how that compared to the amount of the drug in blood plasma.
The company used an "apparent consistent relationship" of the amount of lorcaserin in the brain in relation to the spinal fluid of mice, rats and monkeys. That ratio was used to predict the corresponding amount of the drug in the human brain using the spinal fluid measurements.
Using the new data and previous information, Arena estimates that human brain exposure to the drug is 1.7 times the plasma concentration at normal dose. In rats with a much higher dose, but which didn't have brain cancer, the ratio was 24 times.
Arena noted that its estimates in the study are based on "certain assumptions and extrapolations" and the FDA may have different findings when looking at the raw data. The agency also may not view the company estimates as "reliable or predictive of the safety margin," Arena said in a statement.
Arena is one of three small drug developers that had their weight-loss drug rejected by the FDA in the past year. Vivus Inc. (VVUS) and Orexigen Therapuetics Inc. (OREX) were also turned down by the agency, which raised major safety concerns about the treatments.
Obesity is widespread and a risk factor for many serious health issues, but the FDA has set a high bar for drugs that would be taken indefinitely by millions of patients, many of whom don't have any current health problems.
Past failures--including the fen-phen combination that led to heart-valve problems in some patients--serve as a reminder that safety is the primary concern at the agency. On Monday, Vivus said its retrospective study--analyzing already-collected data--on the birth-defect risk on a component of Qnexa is continuing. Vivus expects the results in the fourth quarter and plans to refile for FDA approval. Qnexa is under review in Europe.
In June, Orexigen suspended U.S. development of Contrave after the FDA asked for additional clinical testing that Orexigen says isn't necessary or feasible.